An automatic transmission is a device, which changes gear ratios automatically, according to the increase or decrease in speed and load of the engine. This ensures that the engine is running at its efficient speed to deliver maximum efficiency. There are two main types of automatic transmissions, the planetary gear type and the continuously variable type. This report gives a description about the working and the components present.  

A transmission is a device that is used to provide a set of discrete angular velocity outputs from a constant velocity source. It is connected to the output of the engine and delivers the power from the engine to the drive wheels. The transmission uses gears to make more effective use of the engines torque and to keep the engine operating at an appropriate speed

An automobile engine runs at its best efficiency at a certain Revolutions Per Minute (RPM) range and it is the transmission's job to make sure that the power is delivered to the wheels while keeping the engine within that range. It does this through various gear combinations. In first gear, the engine turns much faster in relation to the drive wheels, while in high gear the engine is loafing even though the car may be travelling at higher speeds. In addition to the various forward gears, a transmission also has a neutral position which disconnects the engine from the drive wheels, and reverse, which causes the drive wheels to turn in the opposite direction allowing to reverse the direction of the car.

An automatic transmission is much easier to drive than a manual transmission, because they do not have a clutch pedal or gearshift lever. An automatic transmission does the work all by itself. The first automatic transmission appeared in 1939. Automatic transmissions automatically change to higher and lower gear ratios with changes in the speed of the car and the load on the engine. These transmissions are also aware of how far down the accelerator have been pushed, and shift accordingly.